Heavy and Light cruisers, both powerful ships in their proper roles, both perfected by the Japanese navy. Among the most noteworthy of the Japanese Heavy cruisers were the Mogami class, Atago, Tone(famous for launching the late searchplane that flew right over the US forces at Midway and did nothing about it), and Aoba. While these ships were used extensively in the Southern operations of late 41/early 42, they later served under the flag of Kurita at Leyte, and fought bravely against numerically superior forces, mostly escorting the carriers and archaic battleships, and bombarding enemy coastal facilities. They spent the dying days of the war like all Japanese ships (save for Yamato), siting in the shallow harbors of Japan proper, devoid of fuel, and awaiting the end. The end finally came in massive US carrier strikes which sank or heavially damaged anything on the water in the Inland sea.
Light cruisers shared a similar role with their heavier and more powerful counterparts, in that they acted at escorts. Common Japanese practice at Midway, and in the Solomons was to lead a pack of destroyers with a Light cruiser. It was in this area that all cruisers, heavy and light, proved themselves in combat, shelling it out night after night in "The Slot". Aside from the massive firefights between the Kongo class BattleCRUISERS, and US battleships, all of the surface fighting in this area was primarally between cruisers. The most famous Light Cruiser Admiral is probabally Razio Tanaka, commander of landing forces at Midway aboard Jintsu, and later on that same ship, he commanded the famed "Tokyo Express" supply operations at Guadacanal. This was the only real noteworthy operation of light crusiers in the second world war, with Jintsu perhaps being the most famous of all light cruisers. In the end, light cruisers proved to be little more than the heavier destroyers than they were, fast, agile and well armed, they were more than a match for any small craft in the water.
I believe that the light cruisers would have been better classified at Frigates, and saving the designitation Cruiser for the bigger heavy cruiser models.